The present invention is directed to liquid vaporizer systems and, more specifically, to liquid vaporizer systems for low vapor pressure liquids.
Semiconductor fabrication processes may include the use of chemical vapor deposition (CVD) to deposit a thin film of material on semiconductor wafers. CVD processes are often preferred because of their ability to provide highly uniform layers of film. CVD typically comprises introducing gases into a reaction chamber in the presence of a substrate, wherein the gases react and deposit a film on the substrate surface. Some of the CVD materials originate as liquids, and are evaporated and transported in the gaseous state to the desired reaction chamber for CVD.
Liquid reactant sources are often used with CVD processes. For example, titanium tetrachloride (TiCl.sub.4) is used as a reactant gas in CVD to deposit titanium-containing film layers onto a substrate surface. Tetrakisdimethylamidotitanium (TDMAT), a metal-organic material, also is used in CVD processes.
CVD using TiCl.sub.4 and TDMAT typically involves the vaporization of liquid TiCl.sub.4 or TDMAT and the transportation of the gaseous TiCl.sub.4 or TDMAT to the reaction chamber using a carrier gas. Care must be exercised to fully vaporize the liquid compound. If the compound is not fully vaporized and is thus delivered to the reaction chamber as a gas/liquid mixture, liquid compounds in the reaction chamber can lead to poor uniformity of the deposited film and other undesired process results. This also can cause poor repeatability wafer to wafer because liquid droplets deposited on the walls of the process piping can later evaporate, causing fluctuations in vapor concentration in the reaction chamber. Once fully vaporized, care also must be exercised to maintain the compound in a gaseous state while it is being transported to the reaction chamber. Condensation of TiCl.sub.4 or TDMAT can lead to undesirable deposition process variability and possibly the failure of line components.
The vaporization of TDMAT presents unique problems, in part due to the fact that TDMAT has a low vapor pressure. It is desirable, therefore, to provide an efficient mechanism for fully vaporizing TDMAT metal-organic compound, and for transporting the gaseous compound to the reaction chamber while avoiding the condensation of TDMAT liquid out of the gas.